A radio frequency (RF) signal includes useful information that is modulated onto a carrier signal. An RF receiver retrieves the useful information from the RF signal. RF receivers are used in a wide variety of applications such as television transmission, cellular telephones, pagers, global positioning systems (GPS), cable modems, cordless phones, satellite radios, and the like. As used herein, an RF signal means an electro-magnetic signal having a frequency in a spectrum from about 3 kilohertz (kHz) to thousands of gigahertz (GHz), regardless of the medium through which such signal is conveyed. Thus an RF signal may be transmitted through air, free space, coaxial cable, fiber optic cable, etc.
In many broadcast RF transmission systems, the frequency spectrum is relatively wide and is divided into separate channels that include different information. A television receiver receives the wide spectrum RF signal, mixes a desired channel to a convenient intermediate frequency (IF) to make it easier to filter, and then convert it to baseband where the information may be processed further. For example, a television receiver may translate a channel in the frequency spectrum of 48 megahertz (MHz) to 870 MHz to an intermediate frequency of 44 MHz.
Often, the RF signal power level in a particular channel is low, and needs to be amplified before being mixed or otherwise processed in the receiver. Thus a television receiver typically includes one or more low-noise amplifiers to amplify the received signal prior to mixing. However, to provide linear gain, a wide dynamic range, and a large gain range in the presence of small and large signals, television receivers typically employ several narrow band low-noise amplifiers to cover the full frequency spectrum, and it has been difficult to design high quality low-noise amplifiers for wideband applications that provide the desired performance.
What is needed, then, are wideband low-noise amplifier designs for applications such as television receivers that retain the high performance of discrete low-noise amplifiers.
The use of the same reference symbols in different drawings indicates similar or identical items.